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Question #44606

Difficulty: 8/10 | 🟢 Free

The Question

Consider the mono-metallic complex $\ce{[\eta^6-(C6H5-NH-C6H5)]Cr(CO)3}$ , where only one phenyl ring (Ring A) is coordinated to the chromium center, while the other (Ring B) remains uncoordinated. This complex undergoes electrophilic aromatic bromination using 1 equivalent of $\ce{Br2 / FeBr3}$ at 298 K. Assuming the organometallic framework remains intact and N-bromination is reversible, identify the major thermodynamically stable product.

Options

A.
$\ce{[\eta^6-(C6H5)-NH-(4-Br-C6H4)]Cr(CO)3}$
B.
$\ce{[\eta^6-(C6H5)-NH-(3-Br-C6H4)]Cr(CO)3}$
C.
$\ce{[\eta^6-(4-Br-C6H4)-NH-(C6H5)]Cr(CO)3}$
D.
$\ce{[\eta^6-(2-Br-C6H4)-NH-(C6H5)]Cr(CO)3}$

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Exception_Exposure

Learn to identify edge cases and boundary exceptions that JEE examiners hide in math problems.

Concepts Behind This Question

Synergic Bonding in Carbonyls|Electrophilic Substitution Control|Aniline Resonance Pitfalls

Why This Question Is Tricky

Common Mistakes

The trap tests the 'Aniline Resonance Pitfall' in an organometallic context.

Students typically memorize that nitrogen substituents (like $-\ce{NH}-$ ) are strong +M donors and direct EAS to the ortho/para positions.

However, the hidden variable is the synergic back-bonding of the $\ce{Cr(CO)3}$ group, which makes the coordinated ring so electron-deficient that it completely monopolizes the nitrogen lone pair.

This overrides the standard resonance effect, forcing the $-\ce{NH}-$ group to act as a meta-directing -I substituent towards the uncoordinated ring.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Coordination Compounds - Class 12
Concept	Synergic Bonding in Carbonyls
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free